Reduce candidate window flickering.

chrome/browser/chromeos/input_method/candidate_window.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/chromeos/input_method/candidate_window.h"
 
 #include <algorithm>
 #include <string>
 #include <vector>
 
@@ skipping 758 matching lines @@
     : selected_candidate_index_in_page_(0),
       parent_frame_(parent_frame),
       preedit_area_(NULL),
       header_area_(NULL),
       candidate_area_(NULL),
       footer_area_(NULL),
       previous_shortcut_column_size_(0, 0),
       previous_candidate_column_size_(0, 0),
       previous_annotation_column_size_(0, 0),
       is_suggestion_window_location_available_(false),
+      should_show_upper_side_(false),
       was_candidate_window_open_(false) {
 }
 
 CandidateWindowView::~CandidateWindowView() {
 }
 
 void CandidateWindowView::Init() {
   // Set the background and the border of the view.
   set_background(
       views::Background::CreateSolidBackground(kDefaultBackgroundColor));
@@ skipping 93 matching lines @@
 void CandidateWindowView::ShowPreeditText() {
   preedit_area_->Show();
   UpdateParentArea();
 }
 
 void CandidateWindowView::UpdatePreeditText(const std::string& utf8_text) {
   preedit_area_->SetText(utf8_text);
 }
 
 void CandidateWindowView::ShowLookupTable() {
+  if (!candidate_area_->IsShown())
+    should_show_upper_side_ = false;
   candidate_area_->Show();
   UpdateParentArea();
 }
 
 void CandidateWindowView::NotifyIfCandidateWindowOpenedOrClosed() {
   bool is_open = IsCandidateWindowOpen();
   if (!was_candidate_window_open_ && is_open) {
     FOR_EACH_OBSERVER(Observer, observers_, OnCandidateWindowOpened());
   } else if (was_candidate_window_open_ && !is_open) {
     FOR_EACH_OBSERVER(Observer, observers_, OnCandidateWindowClosed());
@@ skipping 334 matching lines @@
   frame_bounds.set_y(std::max(frame_bounds.y(), screen_bounds.y()));
 
   // Handle overflow at the right.
   const int right_overflow = frame_bounds.right() - screen_bounds.right();
   if (right_overflow > 0) {
     frame_bounds.set_x(frame_bounds.x() - right_overflow);
   }
 
   // Handle overflow at the bottom.
   const int bottom_overflow = frame_bounds.bottom() - screen_bounds.bottom();
-  if (bottom_overflow > 0) {
+
+  // To avoid flickering window position, the candidate window should be shown
+  // on upper side of composition string if it was shown there.
+  if (should_show_upper_side_ || bottom_overflow > 0) {
     frame_bounds.set_y(frame_bounds.y() - height - frame_bounds.height());
+    should_show_upper_side_ = true;
   }
 

[Yusuke Sato, 2012/06/08 07:42:26]

I think you should do 

if (should_show_upper_side && top_overflow) {
  frame_bounds.set_y(...);
  should_show_upper_side_ = false;
}

here since the user might scroll the text area during composition. For now,
please add 'TODO(nona): check top_overflow here' or something similar.

[Seigo Nonaka, 2012/06/08 07:51:00]

Done.

   // Move the window per the cursor location.
   // SetBounds() is not cheap. Only call this when it is really changed.
   if (frame_bounds != old_bounds)
     parent_frame_->SetBounds(frame_bounds);
 }
 
 int CandidateWindowView::GetHorizontalOffset() {
   // Compute the horizontal offset if the lookup table is vertical.
   if (!candidate_views_.empty() &&
       lookup_table_.orientation == InputMethodLookupTable::kVertical) {
@@ skipping 495 matching lines @@
 }
 
 // static
 CandidateWindowController*
 CandidateWindowController::CreateCandidateWindowController() {
   return new CandidateWindowControllerImpl;
 }
 
 }  // namespace input_method
 }  // namespace chromeos